Montana class ships

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paul.mercer
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Montana class ships

Postby paul.mercer » Fri Sep 15, 2017 9:34 pm

Gentlemen,
I'm sure this has been raised before but I cannot seem to find it,
Were the 'Montana' class (if built) just an elongated 'Iowa' with an extra turret, or were they built to a heavier and stronger specification i.e. more armour etc?

OpanaPointer
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Re: Montana class ships

Postby OpanaPointer » Fri Sep 15, 2017 11:40 pm


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Alberto Virtuani
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Re: Montana class ships

Postby Alberto Virtuani » Sat Sep 16, 2017 7:48 am

Hi OpanaPointer,
thanks, very interesting link, especially for Panama locks and US knowledge of Yamato specs. :clap:

I must admit that I'm quite ignorant about both Iowa and Montana armor designs, I just have these armor schemes, that look anyway been taken at different hull levels (Iowa at magazine/turret and Montana at boiler rooms level....) and that just confirm that the 2 classes had completely different armor conceptions.

Montana_vs_Iowa.jpg
Montana_vs_Iowa.jpg (36.32 KiB) Viewed 305 times

Can someone confirm/correct these schemes and provide some comments about their efficiency (e.g at which distance/inclination would Montana have been immune to her own and to Yamato's guns?) ?

Bye, Alberto
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Dave Saxton
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Re: Montana class ships

Postby Dave Saxton » Sat Sep 16, 2017 3:15 pm

Alberto Virtuani wrote:
Montana_vs_Iowa.jpg

Can someone confirm/correct these schemes and provide some comments about their efficiency (e.g at which distance/inclination would Montana have been immune to her own and to Yamato's guns?


I don't know what the 17" thick tapered strake is on the Iowa schem but that is not correct.* The Iowa main armoured deck is also not 5.5"-6". It was (outboard) 120mm (4.7") plates laid on top of a, as I recall, 19mm structural deck. This equates to 122mm effective. Taking the above 38mm yaw deck (yes I'm going to call it that) into account using Krupp methodology, the total effective thickness of the deck protection is about 140mm. This is confirmed by the USN IZ calculations of providing deck protection out to 31,000 yards against the West Virginia 16"/45 firing the 2240 lb shell. ( The deck penetration of the 16"/50 firing the 2700 lb shell is about the same and also about the same for Yamato's gun).

Assuming similar construction design of the armoured deck (the structural deck component would need to be thicker because of the greater length), the main armoured deck of Montana would be about 160mm effective, and the deck system taking the yaw deck into account it would be about 192mm effective, which is only slightly inferior to Yamato. This should be good out to 33,000 yards (`30km) vs Yamato's gun.

The Montana armour scheme is a return to the general North Carolina/Washington scheme, but thicker. The NC scheme was extremely vulnerable to under water shell hits, because the main belt was shallow and sloped, but it had a very good torpedo defense system. The Iowa/Sodak system was much less vulnerable to under water shell hits because of the lower belt extension, but this also would have compromised the effectiveness of the TDS. The Montana design contained a lower belt inboard of the TDS, so the advantages of NC scheme could be retained, but the vulnerability of the scheme to under water shell hits ameliorated.

* Maybe it represents the barbets, but they should not be at the midships cross section.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

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Re: Montana class ships

Postby RobertsonN » Sat Sep 16, 2017 4:18 pm

A point about Montana's protection scheme which puzzles me. I have a copy of a document listing official IZ values for US battleships (C-BB/S1-1 of 13 July 1942) against 16 in 2240 lb shells with an MV = 2520 fps. The inner limit for BB 61 (Iowa) is given as 17600 yds and that for BB 67 (Montana) as 16500 yds. But Montana was to have had a 16 in belt, much thicker than Iowa at 12.2 in, both sloped at 19 deg. True the Iowa also has a 1.5 in outer hull, which adds only a little to the overall protection according to any of the usual formulas. There is also the possibility that the outer skin acted as a decapping layer, which would considerably increase the protection offered and indeed prevent effective penetration by intact shells. But I am sceptical that the outer skin was thick enough to reliably decap incoming shells, particularly at the obliquities related to the inner limit of the IZ. And AFAIK no historical sources or serious secondary ones ever mention decapping in this context. But that leaves the problem of the gain of only 1100 yds for a 3.8 in thicker belt. Some of the difference might come from a significantly lower quality of the thicker armor. Any other ideas?

Neil Robertson

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Re: Montana class ships

Postby paul.mercer » Sat Sep 16, 2017 5:05 pm

OpanaPointer wrote:https://www.warhistoryonline.com/guest-bloggers/3-myths-montana-class-battleships.html

Thanks very much, it made most interesting reading.
Paul

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Alberto Virtuani
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Re: Montana class ships

Postby Alberto Virtuani » Sat Sep 16, 2017 6:20 pm

Dave Saxton wrote: "Maybe it (17") represents the barbets, but they should not be at the midships cross section"

Hi Dave,
thanks a lot for all the info and yes, I think it represent the barbette because the IOWA is depicted only for her left side, therefore the strake is the barbette.


Robertson wrote: "that leaves the problem of the gain of only 1100 yds for a 3.8 in thicker belt"

Quite a puzzle. I don't thik it makes sense to use "bad" steel to increase weight for almost nothing. Are you sure that for Montana (as they were designed to withstand their own guns) the IZ graph is not referred to the "super-heavy" 16" shell ?


Bye, Alberto
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Dave Saxton
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Re: Montana class ships

Postby Dave Saxton » Sat Sep 16, 2017 6:51 pm

RobertsonN wrote:A point about Montana's protection scheme which puzzles me. I have a copy of a document listing official IZ values for US battleships (C-BB/S1-1 of 13 July 1942) against 16 in 2240 lb shells with an MV = 2520 fps. The inner limit for BB 61 (Iowa) is given as 17600 yds and that for BB 67 (Montana) as 16500 yds. But Montana was to have had a 16 in belt, much thicker than Iowa at 12.2 in, both sloped at 19 deg. True the Iowa also has a 1.5 in outer hull, which adds only a little to the overall protection according to any of the usual formulas. There is also the possibility that the outer skin acted as a decapping layer, which would considerably increase the protection offered and indeed prevent effective penetration by intact shells. But I am sceptical that the outer skin was thick enough to reliably decap incoming shells, particularly at the obliquities related to the inner limit of the IZ. And AFAIK no historical sources or serious secondary ones ever mention decapping in this context. But that leaves the problem of the gain of only 1100 yds for a 3.8 in thicker belt. Some of the difference might come from a significantly lower quality of the thicker armor. Any other ideas?

Neil Robertson


I think this has to do with the fact that the effectiveness of armour doesn't increase proportionally with increased thickness. G&D allude to this in their chapter on the Bismarck class when they mention that the Germans determined that about 320 mm single plate face hardened armour was the point of diminishing returns in terms effectiveness. After 320mm each additional thickness buys less per weight invested. So 16" only buys a marginal increase in IZ compared to 12".

Note that on other end the additional 2" effective of deck protection only bought about 2,000 yards of IZ. The primary reason is that the deck penetration capabilities of AP shells increases exponentially as the angle fall increases. Moreover, 150mm for a single plate is about the point of diminishing returns for homogeneous armour.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

RobertsonN
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Re: Montana class ships

Postby RobertsonN » Sat Sep 16, 2017 7:23 pm

Yes, this does look more plausible in thinking about it further.

There was an advantage of 1100 yds, which would have needed about an inch of protection. The Americans in their calculations added 0.7 times the strength of secondary protection to the main protection so here the hull skin in Iowa adds 0.7 x 1.5 in = 1.05 in. Putting these together gives

12.2 + 1.0 + 1.05 = 14.25 in

and since in Montana 16.1 in gives this protection, the relative quality of the thick belt to the thinner one would be 14.25/16.1 = 0.885. Looking at it another way if the figure of merit of the Iowa's belt were 2.8 then that of Montana would be 2.8 x 0.885 = 2.48,

Neil Robertson

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Re: Montana class ships

Postby paul.mercer » Fri Sep 22, 2017 8:46 pm

Gentlemen,
Many thanks for the info.
How heavy were the 'Montana's' in comparison with the Yamato's and in your expert opinions, would they have been (if they had been built) the better and more powerful ship?


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